1. Field of the Invention
Embodiments of the invention relate to feedthroughs for optical waveguides, and more particularly, to hermetically sealed feedthroughs suitable for use in high pressure, high temperature, and/or other harsh environments.
2. Description of the Related Art
In many industries and applications, there exists a need to have optical waveguides penetrate a wall, bulkhead, or other feedthrough member wherein a relatively high fluid or gas differential pressure exists across the feedthrough member. In addition, one or both sides of the feedthrough member may be subjected to relatively high temperatures and other harsh environmental conditions, such as corrosive or volatile gas, fluids and other materials. However, several problems exist that are associated with constructing such an optical fiber feedthrough.
One of these problems relates to susceptibility of glass fiber to damage and breakage due to flexibility based on a small size of the fiber, brittle nature of glass material, and presence of a significant stress concentration at the point where the fiber enters and exits the feedthrough. Another problem with sealing an optical fiber occurs due to fused silica material of which the optical fiber is made having a low thermal expansion rate compared to most engineering materials, including metals, sealing glasses and epoxy. This difference in coefficients of thermal expansion greatly increases the thermal stress problem at any glass-to-sealing material interface. For example, epoxy used to seal and fill around the fiber may due to thermal changes break its bond with surrounding metal surfaces and/or the fiber, thereby creating potential leak paths. Such thermal changes may occur in use, during transport that may be in an aircraft, or even at manufacturing where the epoxy may be molded at increased temperatures prior to cooling.
One technique used to produce optical fiber feedthroughs is the use of a sealed window with an input and an output lensing system. In this technique, the optical fiber must be terminated on each side of a pressure-sealed window, thus allowing the light to pass from the fiber into a lens, through the window, into another lens, and finally into the second fiber. The disadvantages associated with this system include the non-continuous fiber path, the need to provide two fiber terminations with mode matching optics, thus increasing manufacturing complexity and increasing the light attenuation associated with these features.
Therefore, a need exists for an improved optical waveguide feedthrough assembly.